1. Field of the Invention
The present invention relates to wearable electronic devices. In particular, the invention concerns a wrist-worn device, such as a wristop computer, which has an antenna for communicating wirelessly with other electronic devices. In addition, the invention concerns a method for the manufacture of an antenna for wearable devices.
2. Description of Related Art
Antennas have been assembled into wristop computers for some time for allowing wireless data transfer into and out of the device. However, incorporating an antenna into a wearable device is a challenging task due to size limitations, great amount of electronic components in proximity to each other and due to the closeness of human body.
The patent application US 2002/0098807 discloses a wrist device with an integrated loop antenna. The loop is placed in the same plane with other electronic circuitry of the device such that some of the electronics is located inside the antenna loop, whereby the electronic circuitry act as a ground plane for the antenna.
Loop-type antennas are also disclosed in the U.S. Pat. Nos. 5,768,217, 5,926,144 and 6,278,873.
Slot antennas can be used instead of conventional loop or dipole antennas due to their ability of producing and sensing alternating electromagnetic fields. The field produced by the a slot antenna is very similar in form to that produced by a dipole antenna having equal dimensions, with the exception that the polarization directions of the electric and magnetic fields are interchanged.
A cellular phone having a slot antenna for short-range communication is disclosed in document U.S. Pat. No. 6,282,433. The antenna is used for subscribing directly to a remote computer or to a local area network (LAN).
U.S. Pat. No. 5,699,319 discloses a wrist-watch, which has a built-in dipole antenna or a slot antenna. The antenna is housed between two casings, one of which forms the outer surface of the watch and the other of which houses electronic and mechanical parts of the device. The antenna is formed as a separate element by applying conductive material to an insulator in order to form a suitable antenna pattern.
A major drawback of the wearable devices referred to above is that because the antenna is located deep inside the housing of the device, conductive materials can not be used in the housing of the device due to the resulting attenuation of the signal. Thus, the described structures can not be used in metal-cased or metal-covered devices. In addition, antenna takes a lot of space inside the device and couples easily to the circuitry of the device, whereby the placing of the parts has to be made taking into account the proximity of the antenna.